* [PATCH v2] socket: Use may_alias on sockaddr structs (bug 19622)
@ 2024-05-07 19:54 Florian Weimer
2024-05-07 19:57 ` Jakub Jelinek
0 siblings, 1 reply; 2+ messages in thread
From: Florian Weimer @ 2024-05-07 19:54 UTC (permalink / raw)
To: libc-alpha; +Cc: Jakub Jelinek, Marek Polacek, Sam James
This supports common coding paddings. The GCC C front end before
version 7 rejects the may_alias attribute on a struct definition
if it was not present in a previous forward declaration, so this
attribute can only be conditionally applied.
This implements the spirit of the change in Austin Group issue 1641.
Suggested-by: Marek Polacek <polacek@redhat.com>
Suggested-by: Jakub Jelinek <jakub@redhat.com>
---
v2: Mention Austing Group issue 1641. Correct the GCC version range.
The C front end was changed early in the 7 release cycle.
bits/socket.h | 4 ++--
inet/netinet/in.h | 8 +++++---
misc/sys/cdefs.h | 9 +++++++++
socket/sys/un.h | 2 +-
sysdeps/mach/hurd/bits/socket.h | 4 ++--
sysdeps/unix/sysv/linux/bits/socket.h | 4 ++--
sysdeps/unix/sysv/linux/net/if_packet.h | 2 +-
sysdeps/unix/sysv/linux/netash/ash.h | 2 +-
sysdeps/unix/sysv/linux/neteconet/ec.h | 2 +-
sysdeps/unix/sysv/linux/netiucv/iucv.h | 2 +-
10 files changed, 25 insertions(+), 14 deletions(-)
diff --git a/bits/socket.h b/bits/socket.h
index 13de124bac..772074d52a 100644
--- a/bits/socket.h
+++ b/bits/socket.h
@@ -149,7 +149,7 @@ enum __socket_type
#include <bits/sockaddr.h>
/* Structure describing a generic socket address. */
-struct sockaddr
+struct __attribute_struct_may_alias__ sockaddr
{
__SOCKADDR_COMMON (sa_); /* Common data: address family and length. */
char sa_data[14]; /* Address data. */
@@ -166,7 +166,7 @@ struct sockaddr
#define _SS_PADSIZE \
(_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
-struct sockaddr_storage
+struct __attribute_struct_may_alias__ sockaddr_storage
{
__SOCKADDR_COMMON (ss_); /* Address family, etc. */
char __ss_padding[_SS_PADSIZE];
diff --git a/inet/netinet/in.h b/inet/netinet/in.h
index fa57b61079..f684be5beb 100644
--- a/inet/netinet/in.h
+++ b/inet/netinet/in.h
@@ -244,7 +244,7 @@ extern const struct in6_addr in6addr_loopback; /* ::1 */
/* Structure describing an Internet socket address. */
-struct sockaddr_in
+struct __attribute_struct_may_alias__ sockaddr_in
{
__SOCKADDR_COMMON (sin_);
in_port_t sin_port; /* Port number. */
@@ -257,9 +257,11 @@ struct sockaddr_in
- sizeof (struct in_addr)];
};
-#if !__USE_KERNEL_IPV6_DEFS
+#if __USE_KERNEL_IPV6_DEFS
+struct __attribute_struct_may_alias__ sockaddr_in6;
+#else
/* Ditto, for IPv6. */
-struct sockaddr_in6
+struct __attribute_struct_may_alias__ sockaddr_in6
{
__SOCKADDR_COMMON (sin6_);
in_port_t sin6_port; /* Transport layer port # */
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 2e8279a2c7..32fc70bf0e 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -874,4 +874,13 @@ _Static_assert (0, "IEEE 128-bits long double requires redirection on this platf
# define __attribute_returns_twice__ /* Ignore. */
#endif
+/* Mark struct types as aliasable. Restricted to compilers that
+ support forward declarations of structs in the presence of the
+ attribute. */
+#if __GNUC_PREREQ (7, 0) || defined __clang__
+# define __attribute_struct_may_alias__ __attribute__ ((__may_alias__))
+#else
+# define __attribute_struct_may_alias__
+#endif
+
#endif /* sys/cdefs.h */
diff --git a/socket/sys/un.h b/socket/sys/un.h
index bf03b7d6ce..ff9cbd6efa 100644
--- a/socket/sys/un.h
+++ b/socket/sys/un.h
@@ -26,7 +26,7 @@
__BEGIN_DECLS
/* Structure describing the address of an AF_LOCAL (aka AF_UNIX) socket. */
-struct sockaddr_un
+struct __attribute_struct_may_alias__ sockaddr_un
{
__SOCKADDR_COMMON (sun_);
char sun_path[108]; /* Path name. */
diff --git a/sysdeps/mach/hurd/bits/socket.h b/sysdeps/mach/hurd/bits/socket.h
index 3e72f9fa93..b5eeac3731 100644
--- a/sysdeps/mach/hurd/bits/socket.h
+++ b/sysdeps/mach/hurd/bits/socket.h
@@ -153,7 +153,7 @@ enum __socket_type
#include <bits/sockaddr.h>
/* Structure describing a generic socket address. */
-struct sockaddr
+struct __attribute_struct_may_alias__ sockaddr
{
__SOCKADDR_COMMON (sa_); /* Common data: address family and length. */
char sa_data[14]; /* Address data. */
@@ -170,7 +170,7 @@ struct sockaddr
#define _SS_PADSIZE \
(_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
-struct sockaddr_storage
+struct __attribute_struct_may_alias__ sockaddr_storage
{
__SOCKADDR_COMMON (ss_); /* Address family, etc. */
char __ss_padding[_SS_PADSIZE];
diff --git a/sysdeps/unix/sysv/linux/bits/socket.h b/sysdeps/unix/sysv/linux/bits/socket.h
index 86444f0018..5ab19a8c08 100644
--- a/sysdeps/unix/sysv/linux/bits/socket.h
+++ b/sysdeps/unix/sysv/linux/bits/socket.h
@@ -181,7 +181,7 @@ typedef __socklen_t socklen_t;
#include <bits/sockaddr.h>
/* Structure describing a generic socket address. */
-struct sockaddr
+struct __attribute_struct_may_alias__ sockaddr
{
__SOCKADDR_COMMON (sa_); /* Common data: address family and length. */
char sa_data[14]; /* Address data. */
@@ -194,7 +194,7 @@ struct sockaddr
#define _SS_PADSIZE \
(_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
-struct sockaddr_storage
+struct __attribute_struct_may_alias__ sockaddr_storage
{
__SOCKADDR_COMMON (ss_); /* Address family, etc. */
char __ss_padding[_SS_PADSIZE];
diff --git a/sysdeps/unix/sysv/linux/net/if_packet.h b/sysdeps/unix/sysv/linux/net/if_packet.h
index 9ffb69b508..c17e1c23c5 100644
--- a/sysdeps/unix/sysv/linux/net/if_packet.h
+++ b/sysdeps/unix/sysv/linux/net/if_packet.h
@@ -26,7 +26,7 @@
From Linux 2.1 the AF_PACKET interface is preferred and you should
consider using it in place of this one. */
-struct sockaddr_pkt
+struct __attribute_struct_may_alias__ sockaddr_pkt
{
__SOCKADDR_COMMON (spkt_);
unsigned char spkt_device[14];
diff --git a/sysdeps/unix/sysv/linux/netash/ash.h b/sysdeps/unix/sysv/linux/netash/ash.h
index 7d885d17cc..7a6ff50b17 100644
--- a/sysdeps/unix/sysv/linux/netash/ash.h
+++ b/sysdeps/unix/sysv/linux/netash/ash.h
@@ -22,7 +22,7 @@
#include <features.h>
#include <bits/sockaddr.h>
-struct sockaddr_ash
+struct __attribute_struct_may_alias__ sockaddr_ash
{
__SOCKADDR_COMMON (sash_); /* Common data: address family etc. */
int sash_ifindex; /* Interface to use. */
diff --git a/sysdeps/unix/sysv/linux/neteconet/ec.h b/sysdeps/unix/sysv/linux/neteconet/ec.h
index b07a107961..f3132f06ff 100644
--- a/sysdeps/unix/sysv/linux/neteconet/ec.h
+++ b/sysdeps/unix/sysv/linux/neteconet/ec.h
@@ -28,7 +28,7 @@ struct ec_addr
unsigned char net; /* Network number. */
};
-struct sockaddr_ec
+struct __attribute_struct_may_alias__ sockaddr_ec
{
__SOCKADDR_COMMON (sec_);
unsigned char port; /* Port number. */
diff --git a/sysdeps/unix/sysv/linux/netiucv/iucv.h b/sysdeps/unix/sysv/linux/netiucv/iucv.h
index f5fad81751..27151e8bbe 100644
--- a/sysdeps/unix/sysv/linux/netiucv/iucv.h
+++ b/sysdeps/unix/sysv/linux/netiucv/iucv.h
@@ -23,7 +23,7 @@
__BEGIN_DECLS
-struct sockaddr_iucv
+struct __attribute_struct_may_alias__ sockaddr_iucv
{
__SOCKADDR_COMMON (siucv_);
unsigned short siucv_port; /* Reserved */
base-commit: 143ef68b2aded7c794956beddad495af8c7d3251
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v2] socket: Use may_alias on sockaddr structs (bug 19622)
2024-05-07 19:54 [PATCH v2] socket: Use may_alias on sockaddr structs (bug 19622) Florian Weimer
@ 2024-05-07 19:57 ` Jakub Jelinek
0 siblings, 0 replies; 2+ messages in thread
From: Jakub Jelinek @ 2024-05-07 19:57 UTC (permalink / raw)
To: Florian Weimer; +Cc: libc-alpha, Marek Polacek, Sam James
On Tue, May 07, 2024 at 09:54:14PM +0200, Florian Weimer wrote:
> --- a/misc/sys/cdefs.h
> +++ b/misc/sys/cdefs.h
> @@ -874,4 +874,13 @@ _Static_assert (0, "IEEE 128-bits long double requires redirection on this platf
> # define __attribute_returns_twice__ /* Ignore. */
> #endif
>
> +/* Mark struct types as aliasable. Restricted to compilers that
> + support forward declarations of structs in the presence of the
> + attribute. */
> +#if __GNUC_PREREQ (7, 0) || defined __clang__
I'd use (7, 1) here, because pedantically there were some 7.0.0 snapshots
which didn't support it.
7.1.0 and later do support it though.
Otherwise LGTM.
Thanks.
Jakub
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